A heterogeneous network is attracting attention in current 3GPP-LTE (3rd generation partnership project radio access network long term evolution) (see, for example, Non-Patent Literature 1, 2, 3, and 4).
The heterogeneous network employs not only “a macro base station (a macro cell)” (it may be referred to as a large cell base station) but also “a pico base station (a pico cell)” (it may be referred to as a small cell base station) in order to respond to an increased capacity in a cellular network. The macro base station covers a large area (for example, a coverage area having a cell radius of several kilometers) and the pico base station covers a small area (for example, a coverage area having a cell radius of several tens of meters).
As shown in FIG. 1, one or more pico base stations (“Pico” shown in FIG. 1) are allocated in a service area for the macro base station (“Macro” shown in FIG. 1) in the heterogeneous network, for example. The macro base station covers a larger service area than the pico base station, and is therefore effective for the improvement of an area cover ratio. Meanwhile, the pico base station covers a service area smaller than that of the macro base station, and therefore allows a distance, at which the same frequency (a frequency reuse distance) can be reused, to be shorter. Thus, a larger number of cells can be allocated in a certain area to effectively improve the use efficiency of a frequency. Accordingly, the heterogeneous network is directed to allow both a high area cover rate and a high use efficiency of a frequency through complementary allocation of the macro base station and the pico base station.
A base station which connects with only a group of terminals (a closed subscriber group) having an access right in advance may be distinguished from the pico base station and be referred to as “a femto base station (a femto cell)” among base stations covering small cells as a coverage area. For simplicity of explanation, the pico base station and the femto base station are simply represented as “a pico base station” without distinguishing the pico base station and the femto base station in the following explanation.